On the top of the heater at the rear center, you will see a depression with a hexagonal plug in it. That plug is the anode. You will need the proper sized socket, (and a lot of muscle), to unscrew it. Pull the rod out. Try to be as careful as possible since the rod could be coated with a jelly like substance and the more careful you are the less that will be scraped off as you remove it. Then either replace the anode or use a 3/4" pipe plug to seal the opening.

: I need to replace the anode rod in my Reliance 501 we believe that it is worn out causing a rotten egg odor. But we don't know how to replace it and we can't seem to find the Reliance website.